Ant Control using Boric Acid

Ants are ubiquitous household pests the world over. Several species of ants are known to be invasive species that have spread far beyond their native range. Species like the Pharoah ant (Monomorium pharaonis), Singapore ant (Trichomyrmex destructor), some species of red fire ants (Solenopsis spp), and Ghost ants (Tapinoma melanocephalum) are quite well known around the world. Fortunately, ant control is a much more simple affair compared to termites, and here we’ll look at one of the most widely used methods in ant control – the use of boric acid (or Borax).

Formerly Monomorium destructor but reclassified by scientists to the Trichomyrmex genus in 2015, the Singapore ant (Trichomyrmex destructor) is infamous for not only raiding the rubbish bin, but nesting inside anything as long as it has a hollow compartment. It has a habit of chewing through plastic bags and thin wires, sometimes resulting in damage to electrical devices. It has even been reported to cause short circuits in cars and causing fires in buildings. These are small ants with workers only about 2.5 mm long, so they can squeeze into tiny cavities and nest almost anywhere.

My computer keyboard recently became a target of an invasion of Trichomyrmex destructor, and they were crawling all over my computer table and giving my arms nasty bites and stings. They probably chewed on the internal wiring inside my keyboard because the keys didn’t work so well after they entered it; soon afterwards I had to replace my keyboard that I used for years. These ants are nasty!

Singapore ants have an ability to split off into smaller colonies seeing that each colony typically has many queens and these queens routinely break off with a retinue of workers to form new colonies elsewhere. Also, these new colonies do not fight. Colonies can number in the hundreds of thousands (maybe even more). They are tough to control, and spraying them with bug spray may actually trigger them to split off into smaller colonies.

Enter the use of boric acid….

But first, let’s explain the difference between boric acid and Borax.

Borax and boric acid are similar in that both are compounds of the mineral boron, and yet both are different. Borax is mined from the soil and is used to make preservatives, hand soap, laundry washing powder, and a whole lot of things. Meanwhile, boric acid is a processed crystalline compound of Borax and used in the manufacture of fiberglass, insecticide, antiseptics, and eyewash, among others. For humans, boric acid is more toxic than Borax, although both should not be ingested, even though they are not comparatively as toxic as other insecticides.

Both Borax and boric acid are toxic to termites, ants, cockroaches, and many other insects, with a similar mode of action, although the one that you buy from pharmacies are often likely to be boric acid. Mix this with a bit of peanut butter or honey (if your ants love sweet stuff) and voila, you have a DIY ant bait ready for use. However, remember to only use very weak concentrations, because insects can detect the boric acid and often refuse to feed on the bait (as will be seen below). Commercial formulations often contain only 5% or less of boric acid.

How does boric acid kill ants?

Boric acid weakens and removes the outer waxy coating that covers the exoskeleton of ants (and other insects) when they crawl over it. This wax coating helps the ants retain moisture in their bodies, so when it is diminished, the ants dehydrate and die. When ingested by insects, it goes without saying that boric acid affects their metabolism, and they soon weaken and die.

Since both boric acid and Borax take a while to work, it gives enough time for the ants to share the bait with their nest mates via trophallaxis. Thus, the bait gets spread around indirectly, resulting in a higher kill rate.

Is boric acid bait really effective?

The question arises, is boric acid bait truly effective in ant control? Check out the photos below of my attempt to control these Singapore ants (Trichomyrmex destructor) using a commercially available liquid formulation (containing boric acid).

It must be noted that this infestation was merely a small colony that split off from a much larger one that was roaming outside my home, and they somehow migrated indoors into my home (and then into my computer keyboard).

Also worth noting: This commercial formulation used a sweet honey-like substance as bait, and although it aroused some interest in the ants, they quickly lost interest in it, especially once the bait dried up.

ants feeding on bait containing boric acid

At first, I tried putting the liquid bait in a line along the ant trail, but quickly noticed that it was a bit wasteful, since not many ants were attracted to the bait. Many passing ants simply ignored it.

 

ants feeding on bait containing boric acid

Next I tried placing droplets on the ant trail, which received a relatively better response from the ants.

 

ants feeding on bait containing boric acid

I could never get a great response from these Singapore ants, who probably preferred a more protein-based bait, rather than a sugary one. Nonetheless, by carefully choosing the best locations to place a few droplets, such as this “junction-like” spot which confronts all ants emerging up from below the table, this soon resulted in a big congregation of ants lapping up the poisonously sweet bait. Notice the black dirt on the edge of the bait droplet. These were placed by the ants themselves. See below.

 

singapore ant reaction to bait containing boric acid

After consuming the bait, the ants quickly lose interest and they then appear to be attempting to seal/cover up the bait with dirt particles (even small bits of wood) that they gathered from elsewhere. It’s unclear why they do this. Is it because they are trying to prevent their other nest mates from consuming the bait which they suspect is poison? This behavior happened for all the droplets that I put – the ants would always attempt to cover it in some manner, starting from the edges, and appear to be sealing off the bait droplets all along the edges, if not completely covering it up. This indeed prevented other ants from later consuming the bait.

 

boric acid effect on ants

The ants become terminally ill after consuming boric acid, and many will stay still and then die after some hours.

 

dead ants after poisoned by boric acid

Ants that died would be gathered by their nest mates and disposed off around impromptu ant “graveyards”. I noticed piles of dead ants on my computer table within 36 hours after using the bait for the first time.

 

Conclusion

As the photos show, boric acid does kill ants, but how truly effective it is in getting rid of an ant problem depends largely on two factors.

  • The species of ant. Ants that love sugary substances would need sugary bait, while ants that prefer protein would prefer something with more protein content. Since many commercial formulations use a sugary substance as bait, they may not work so well in those particular cases. Ants that regularly split off into new colonies (like these Singapore ants) would be harder to get rid of as well, because new ones may be constantly coming in.
  • The size of the ant infestation. The larger the colony, the harder and longer to eliminate. If the colony is huge and ranges over a wide area, ant control using bait will not make much of a dent.

In the end, I had to resort to using insecticide spray to finish off the remaining ants because after over one week, the problem was still not resolved. Although the boric acid bait was quite successful in reducing the number of ants crawling on my computer table (by approximately 80%), new ant parties appeared to be constantly coming up the table from newly formed scent trails. The insecticide spray destroyed those scent trails instantaneously and greatly discouraged new ants from further coming into my home. In my particular case, it was a combination of ant bait and insecticide that finally did the job.

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